'78 GS1000 stock VM26 jetting baseline

[BlackStar]

I'm removing VM29 smoothbores and installing the stock VM26's (from salvage yard) after a thorough cleaning. The engine is stock, with a VH 4-1 exhaust with K&N pod filters.
I'm at about 800 ft above sea level.
About where should I be for jetting? Main, Pilot, Needle?

The VM29's have a stripped jet block on the #4 carb where the needle jet threads in (I didn't do it!). I found out today this is a weakness in the VM29's if you are not carefull, so you VM29 guy's be carefull!! Too bad, these carbs are in great condition. I may end up putting them on ebay to re-coup my VM26 costs.

Thanks

 

[KEITH KRAUSE]

If the bike is otherwise tuned correctly, valves, timing, etc, I can suggest some jetting. Be sure to replace the carb inner o-rings during the cleaning. Robert Barr, a member here, sells an excellent VM o-ring kit. Also, replace the manifold o-rings if any doubt. Coat with some hi-temp bearing grease and replace the Phillips screw with Allens and torque the manifolds to 6 ft/lb. Set floats to .94"
The stock jet needles sometimes give inferior results but you can try. DJ jet kits are hard to find anymore with the far better mixing jet needles. Just letting you know.
Use 130 Mikuni mains. The DJ kit provides their own 138 and 142 mains. You don't need the 142's. Because they're sized using a different method, a 138 DJ main is approx' the same as a 130 Mikuni main. A 130 Mikuni main should be perfect for your V&H pipe and K&N filters as the stage 3 138 main jet is designed for exactly those two brands of parts.
Place the jet needle e-clips in the bottom/richest position. That's the only chance the stock needles have of working well. Replace all factory plastic spacers in factory order. Thicker ring on top the clip, thinner spacer below the clip. Test at 1/3 throttle.
Try the stock 15 pilot jet but richen the pilot fuel screws underneath. Stock screw adjustment is typically 3/4 to 1 turn out from LIGHTLY seated. Try 1 1/2 turns. Test at minimal throttle. If no joy by about 2 1/2 turns out, then go to the 17.5 pilots and return the screw to 1 turn out and test/fine tune.
Set the side air screws by using the highest rpm method. They should end up 1 1/2 to 1 3/4 turns out.
REMOVE the 2 floatbowl vent lines to avoid fuel starvation, especially during windy/crosswind days. Leave the ports open. This is mentioned as a requirement in the DJ jet kit info.
A good bench synch followed by a vacuum tool synch is a basic part of the re-jet before testing.
It's late and I took the time to help you out, so please get back to us and let us know how she runs.

 

[Suzuki mad]

Surely there must be a way of saving these carbs rather than replacing them?

Nobody able to get a thread in there?

suzuki mad

 

[BlackStar]

Thanks for the replies. The boots and o-rings are all new from suzuki. Phillips screws have been replaced with SS Socket head cap screws. All else is checked out and good.

I may be able to get the VM29's repaired with a custom made bushing threaded inside and outside. Until then it's VM26's.

 

[BlackStar]

Since you guy's were all kind enough to reply I wanted to get back with you to let you know the status. 1st I was able to get a hold of a Dynojet stage 3 kit.
Stock GS1000 with Mikuni VM26's (stock), K&N pods, V+H 4-1 exhaust.
I'm running the 138 DJ mains
#15 pilots
Fuel screws at 2 1/2 turns out (per DJ)
DJ needles with clip on 2nd groove down with DJ supplied metal washer and stock thick plastic washer on top. Stock thin plastic washer under the clip. DJ instructions were not the clearest here, I hope I got it right.
Still messing with the air screws.
Bike starts and runs great including idle. I don't think I have been on the main jets yet since I'm still working down low. Plugs look OK. Iv'e managed to turn my new headers near the cylinders a light gold in the process of tweaking. No blue, just gold.
Does this all sound in the ballpark?
Thanks all!!

 

[KEITH KRAUSE]

DJ makes a pretty good product but from my experience, I don't know where they come up with those jet needle "base setting" recommendations. Position 1 1/2 for K&N pods and ANY quality pipe??
I've jetted quite a few 70's Suzuki's and Kawasaki's and I've never seen a single one run right with the jet needles in that lean position. DJ does say that the correct needle position can vary as much as 3 full positions but I've never seen that range give good results.
I do keep some records over the years and the leanest jet needle position I've ended up with was with a jetting spacer on top the e-clip in the 4th position from the top, in other words, position "3 1/2", which was with some K&N wannabe's and an RC pipe. That was on a friends 1 year old '79 1000 and I still believe it was a tad lean but he liked it the way it was and didn't want to keep playing with it. The richest needle position I have written down was on a '78 1000 with K&N's/Yosh pipe and 1085 kit. That bike had the DJ needles at position "4 1/2", the e-clips in the 5th position with a jetting spacer on top. So there's a range of 1 full position I've seen.
Something about running lean, some people can't really feel surging and it's a fact that a mixture a little on the lean side will make very good power. It will fool you into thinking things are right. A little lean is fine for some racing but not for a street bike that may be involved in long rides and rides in the city on hot days.
I have to think your bike is running very lean with the jet needles positioned as they are. You spend the most time riding on the needles and they need to be right. The DJ needles regulate sooner than the stockers and anything from about 1/5 throttle to 3/4 is controlled by them. I'd be very surprised if a 1/3 throttle chop showed plug colors anywhere close to tan/tannish-gray, which is what they will look like if jetted correctly. Regardless of info I've read or you've read, todays gas will still color a plug if the mixture is even close to right.
I suggest placing the e-clip in the 4th position. That's the most common position I've noted over the years with your exact mods. Then re-bench synch and follow that with a vacuum tool synch.
As for the pilot fuel screws, 2 1/2 turns out seems too much to me also.
Something closer to 1 1/2 has worked for me in the past.
Just my opinions.

 

[BlackStar]

Thanks for taking the time to reply Keith. I'll reset the needles and get things synced back up and let you know how it runs.
When you perform your vacuum sync. on VM26's do you remove the tops of all 4 carbs and run it per the service manual? This seems to create vacuum leaks and the bike does not run well. The last time I did this I had to pull the carbs back off, and re-mech. sync. them. I had a set of VM29's on the bike for a while, and Sudco / Mikuni recommended mechanical sync. only due to the vacuum leaks created when the top of the carbs are removed. The VM29's and the VM26's are very similar in design in this area, so I'm a little confused.
BTW I'm really beginning to appreciate fuel injection!

 

[KEITH KRAUSE]

There's no other way to synch these carbs. The tops must be off to get to the adjusting screws/holder nuts. Torque the holder nuts at 3.5 ft/lb. There's no vacuum leak of any significance regardless of what you've heard.

 

[BlackStar]

Update / sanity check

1978 GS1000 stock engine and carbs (VM26), V&H 4-1 exhaust, K&N pod filters, 138 DJ Mains, stock #15 pilot jets, DJ needles, New boots and o-rings, 13,000 original miles. Valves and compression good. 2nd owner. My uncle bought it new April 1978.

I'M GETTING THERE!, I Think?

Iv'e reset the DJ needles to the 4th clip position down. I'm at about 1 1/4 turns out on the fuel screws. Air screws adj. for max rpm, sync. good.

The bike idles and runs good. Cylinders 2 and 3 have nice tan plugs which is perfect. Cylinders 1 and 4 are rich and the plugs are black. I thought I had an ignition problem so I went down that path. I've replaced the points/condensers and set the timing with a light, it needed this anyway. Still rich. Coil (stock) primary resistance is about 4 ohms on the 1-4 coil. Secondary resistance was > 400K. This turned out to be a bad spark plug cap on #1. This has been fixed with new caps and now reads in spec., very close to 2-3 sec. resistance. I have also performed the coil relay mod to ensure that I am getting full battery voltage to the primarys. Still rich. The 1-4 plugs always did fire when laying out on the head, I suspected the spark was weak and I suppose it still could be

I've ordered all new floats for the carbs as I am suspect of the floats with them being foam instead of brass and being nearly 30 years old. I normally replace foam floats in automotive carbs for that reason. I don't know if all the floats have the same bouyancy since they may be saturated. The levels were set meticulously but I do not have the adapter to thread into the drain screw holes to verify the actual level. I do not have fuel dripping out of the overflow tubes so it isn't that bad yet. Speaking of the overflow tubes, I have hoses connected to the carb bowl overflows and routed back over the swingarm pivot. On the upper vent fittings, I have left them open, no hoses fitted. New needle and seats were installed at the initial overhaul as well as all new carb o-rings. Choke plungers confirmed down fully.

Am I overlooking anything? If new floats do not work, I'm thinking I might try swaping the coil primary wires and plug wires to see if the rich condition moves to 2-3, if the plug wires reach.

Thank you all for your replies, your support has been tremendous!

I need to post pictures of this bike, it looks great!

Shane

 

[BlackStar]

Here it is almost done, original paint.

 

[KEITH KRAUSE]

Getting late so just a quick reply. I'll try to add later if still needed.
You said "synch is good". Does that mean a good synch with a vacuum tool or just a bench synch? Vacuum tool synch is a must during any re-jet.
Lots of things can cause a suspected rich condition at 1/4, or any, cylinders. Coil is a thought as you've mentioned. A wiring swap should prove without doubt. Leave the plugs in their current order but rinse and wipe them off. Look for frayed/broken wires at the coil terminals. Look for ANY hardening of the leads or possible arcing to frame, etc.
With only 13K, if original, the carbs "shouldn't" have any worn parts such as needle jets/bleedpipes, etc. But possible of course. I understand the floats will be replaced. New float valves and seats were replaced. If you bought any float valves other than genuine Suzuki, it could be a problem. I've seen many brands of cheaper ones operate incorrectly due to poor quality/weak springs. They may be fine, just mentioning that.
Also, you need to mention what throttle position(s) gave you those plug reads. If just general cruising around town, then you're on the pilot circuit a lot and simple leaner pilot fuel screw adjustments may help. The answer MAY be just a 1/4 turn in (CW) on the pilot fuel screws at 1 and 4. Remember, these screws don't have to be exactly uniform. They are for fine tuning each cylinder and it's fairly common to adjust them a little differently from each other. Generally, I've allowed up to 3/8 of a turn difference from the "richest one to the leanest one" to get good overall pilot circuit results. So a 1/4 turn is acceptable. Beyond 3/8 max' difference means something else is wrong though, in my opinion.
I gotta go, will try to add later.